Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Existing hybrid vehicles have a complicated structure combining a conventional internal combustion engine and one or more electric motors. Also, such hybrid vehicles typically use a secondary battery such as a lithium ion battery, which results in significantly increasing their weight and manufacturing costs compared to the conventional vehicles having internal combustion engine.
For example, a series hybrid vehicle includes an engine tuned for running an electric generator for generating electrical energy, and a battery such as a lithium ion battery for storing the electricity from the electric generator and providing the stored electricity to an electric motor for driving wheels. In such a system, the motor torque is sufficiently large for driving the wheels at a low speed, while the efficiency may decrease significantly when the motor is operated to drive the wheels at a high speed. Contrary to the series hybrid vehicle, a parallel hybrid vehicle has been designed to install an electric motor and an internal combustion engine such that they can drive the wheels individually or in cooperation. Also, a series-parallel hybrid vehicle has been developed where one or more electric motors and an internal combustion engine are installed to share the power for driving the wheels. In such a vehicle, however, the installation of more than one electric motor requires a more sophisticated controller and results in cost increase.
As described above, the conventional hybrid vehicles require a complicated controller for controlling one or more motors to drive the wheels with sufficient torque. Also, a high-capacity battery, such as a lithium ion battery, used in powering the electric motors attributes to a significant increase in the manufacturing cost.